Tennis racquets have, for many years, been constructed of wood and in fact is still being used in the construction of some racquets. However, a wooden racque has certain inherent limitations, particularly as regards torsional and bending rigidity, it being generally recognized that these two parameters are mutually dependent in the sense that a wooden racquet designed to have a particular rigidity will have a built-in bending rigidity which may or may not be desirable from the standpoint of optimum racquet strength, flexibility, weight and other factors important to good racquet design.
The idea of forming a racquet of metal so as to overcome some of the deficiencies of wooden racquets is not new. French Pat. No. 800,262 (1936) discloses a metal tennis racquet comprising an alloy of aluminum and magnesium; and formed by casting the racquet in a mould followed by a thermal treatment to give suitable elasticity and resilience. In casting the head-portion of the racquet removable core pieces are assembled in the mould to form apertures in the head-portion for stringing the racquet. U.S. Pat. No. 3,702,189 Galich discloses a one-piece metal tennis racquet formed by casting an aluminum or magnesium alloy in a permanent mould. Stringing apertures are cast in the head-portion or frame and in addition an elongated annular groove is formed in the outer face of the frame for recessing the racquet string. The aforesaid annular groove is alleged to serve both as a means for weight and balance control as well as protective means for shielding the racquet string from abrasion. U.S. Pat. No. 3,702,701 Vaughn et al. discloses a tennis racquet frame formed of opposed, extruded aluminum, tubular sections joined by an integral metal web-portion having stringing apertures therein; and a strip of nylon is assembled on the web-portion to provide grommets for the stringing apertures in the metal web so as to reduce string abrasion. U.S. Pat. No. 3,664,669 Lantem et al. discloses another form of extruded aluminum tennis racquet the head-portion or frame of which comprises a hollow extrusion having a central wall separating the outer wall from a pair of flanges constituting the inner wall of the frame, the flanges being arranged to provide holding means for a plurality of individual, plastic, string-supporting elements designed to provide a relatively large gripping surface, i.e. large radii about which to bend the string so as to eliminate string breakage.
One of the major advantages of forming a racquet frame by casting, as against forming a frame by extrusion, is the freedom to vary the cross section of a cast frame place to place. On the other hand, a die cast metal frame will, in general, have less strength than an extruded frame, and more importantly, a die cast frame is generally subject to localized metal porosity which, when present in the area of the stringing holes of a racquet frame will cause rupture or breakthrough under the high stresses to which a racquet is subjected.
Hence, despite the progress that has been made in the construction of light metal racquets, the problems of achieving optimum strength to weight ratios, optimum stiffness, both longitudinal and torsional, and minimizing the incidence of string breakage; together with the development of production techniques that will ensure low unit cost, have mitigated against substantial acceptance of metal racquets as heretofore designed.